PALS1 is a key regulator of the lateral distribution of tight junction proteins in renal epithelial cells.

The evolutionarily conserved Crumbs (CRB) polarity complex, which consists of the core components CRB3a, PALS1 and PATJ, plays a key role in epithelial cell-cell contact formation and cell polarization. Recently we observed that deletion of one Pals1 allele in mice results in functional haploinsufficiency characterized by renal cysts. To address the role of PALS1 at the cellular level, we generated PALS1 knockout MDCKII cell lines using the CRISPR/Cas9 system. The loss of PALS1 resulted in increased paracellular permeability indicative of an epithelial barrier defect. This barrier defect was associated with a redistribution of several tight junction-associated proteins from bicellular cell-cell contacts to tricellular junctions. The regulation of tight junction protein localization at bicellular junctions by PALS1 was dependent on its interaction with PATJ. Together, our data uncover a critical role of PALS1 in the correct positioning of tight junction proteins to bicellular junctions.